Develop Reference

Android: OpenGL drawing only on one quarter of screen on Exynos devices

Problem.
I have a problem with specific android devices. I'm using native C++ library to draw stuff in my app. For a long time the solution I use worked well on different devices, until I received a negative feedback from Samsung Galaxy S4 user (GT-I9500, Android 4.4.2, Exynos 5410). The result of my OpenGL drawing was corrupted. The texture that usually draw fullscreen in this case was shrinked to a quarter of the screen space and aligned to upper right corner. The background drawn with glClearColor was filling full screen tho. I was able to check on three other S4s - out of total four phones my app the drawing is corrupted only on Exynos devices. The other two had Snapdragon and there were no problems on them.
Code.
I've simmplified the code a bit so I can show it here. The task is basic: draw red background and black fullscreen rectangle on top of it.
Below you can see my drawing method. Data I pass to the shaders don't affect anything in this simplified case.
// Use program
glUseProgram(_shaderProgram);
ERROR_STATUS
//bind quad mesh buffer
glBindBuffer(GL_ARRAY_BUFFER, _vbo);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _ibo);
ERROR_STATUS
//set attribs
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(Vertex), 0);
glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, sizeof(Vertex), (void *) (2 * sizeof(float)));
glEnableVertexAttribArray(0);
glEnableVertexAttribArray(1);
ERROR_STATUS
// Clear background to red
glClear(GL_COLOR_BUFFER_BIT);
glClearColor(1, 0, 0, 1);
glUniform2fv(_scaleUniform, 1, _eyes[0].scale.data);
glUniform1f(_offsetUniform, _eyes[0].offset);
glUniform1f(_offsetYUniform, _eyes[0].offsetY);
BindTextures(TEX);
// Draw
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_SHORT, NULL);
ERROR_STATUS
glDisableVertexAttribArray(0);
glDisableVertexAttribArray(1);
ERROR_STATUS
And here is my ConfigChooser(grafika was great help here).
private static class ConfigChooser implements GLSurfaceView.EGLConfigChooser {
public ConfigChooser(int r, int g, int b, int a, int depth, int stencil) {
mRedSize = r;
mGreenSize = g;
mBlueSize = b;
mAlphaSize = a;
mDepthSize = depth;
mStencilSize = stencil;
}
/* This EGL config specification is used to specify 2.0 rendering.
* We use a minimum size of 4 bits for red/green/blue, but will
* perform actual matching in chooseConfig() below.
*/
private static int EGL_OPENGL_ES2_BIT = 4;
private static int[] s_configAttribs2 =
{
EGL10.EGL_RED_SIZE, 4,
EGL10.EGL_GREEN_SIZE, 4,
EGL10.EGL_BLUE_SIZE, 4,
EGL10.EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT,
EGL10.EGL_NONE
};
public EGLConfig chooseConfig(EGL10 egl, EGLDisplay display) {
/* Get the number of minimally matching EGL configurations
*/
int[] num_config = new int[1];
egl.eglChooseConfig(display, s_configAttribs2, null, 0, num_config);
int numConfigs = num_config[0];
if (numConfigs <= 0) {
throw new IllegalArgumentException("No configs match configSpec");
}
/* Allocate then read the array of minimally matching EGL configs
*/
EGLConfig[] configs = new EGLConfig[numConfigs];
egl.eglChooseConfig(display, s_configAttribs2, configs, numConfigs, num_config);
if (DEBUG) {
printConfigs(egl, display, configs);
}
/* Now return the "best" one
*/
return chooseConfig(egl, display, configs);
}
public EGLConfig chooseConfig(EGL10 egl, EGLDisplay display,
EGLConfig[] configs) {
for(EGLConfig config : configs) {
int d = findConfigAttrib(egl, display, config,
EGL10.EGL_DEPTH_SIZE, 0);
int s = findConfigAttrib(egl, display, config,
EGL10.EGL_STENCIL_SIZE, 0);
// We need at least mDepthSize and mStencilSize bits
if (d < mDepthSize || s < mStencilSize)
continue;
// We want an *exact* match for red/green/blue/alpha
int r = findConfigAttrib(egl, display, config,
EGL10.EGL_RED_SIZE, 0);
int g = findConfigAttrib(egl, display, config,
EGL10.EGL_GREEN_SIZE, 0);
int b = findConfigAttrib(egl, display, config,
EGL10.EGL_BLUE_SIZE, 0);
int a = findConfigAttrib(egl, display, config,
EGL10.EGL_ALPHA_SIZE, 0);
if (r == mRedSize && g == mGreenSize && b == mBlueSize && a == mAlphaSize)
return config;
}
return null;
}
private int findConfigAttrib(EGL10 egl, EGLDisplay display,
EGLConfig config, int attribute, int defaultValue) {
if (egl.eglGetConfigAttrib(display, config, attribute, mValue)) {
return mValue[0];
}
return defaultValue;
}
private void printConfigs(EGL10 egl, EGLDisplay display,
EGLConfig[] configs) {
int numConfigs = configs.length;
Log.w(TAG, String.format("%d configurations", numConfigs));
for (int i = 0; i < numConfigs; i++) {
Log.w(TAG, String.format("Configuration %d:\n", i));
printConfig(egl, display, configs[i]);
}
}
private void printConfig(EGL10 egl, EGLDisplay display,
EGLConfig config) {
int[] attributes = {
EGL10.EGL_BUFFER_SIZE,
EGL10.EGL_ALPHA_SIZE,
EGL10.EGL_BLUE_SIZE,
EGL10.EGL_GREEN_SIZE,
EGL10.EGL_RED_SIZE,
EGL10.EGL_DEPTH_SIZE,
EGL10.EGL_STENCIL_SIZE,
EGL10.EGL_CONFIG_CAVEAT,
EGL10.EGL_CONFIG_ID,
EGL10.EGL_LEVEL,
EGL10.EGL_MAX_PBUFFER_HEIGHT,
EGL10.EGL_MAX_PBUFFER_PIXELS,
EGL10.EGL_MAX_PBUFFER_WIDTH,
EGL10.EGL_NATIVE_RENDERABLE,
EGL10.EGL_NATIVE_VISUAL_ID,
EGL10.EGL_NATIVE_VISUAL_TYPE,
0x3030, // EGL10.EGL_PRESERVED_RESOURCES,
EGL10.EGL_SAMPLES,
EGL10.EGL_SAMPLE_BUFFERS,
EGL10.EGL_SURFACE_TYPE,
EGL10.EGL_TRANSPARENT_TYPE,
EGL10.EGL_TRANSPARENT_RED_VALUE,
EGL10.EGL_TRANSPARENT_GREEN_VALUE,
EGL10.EGL_TRANSPARENT_BLUE_VALUE,
0x3039, // EGL10.EGL_BIND_TO_TEXTURE_RGB,
0x303A, // EGL10.EGL_BIND_TO_TEXTURE_RGBA,
0x303B, // EGL10.EGL_MIN_SWAP_INTERVAL,
0x303C, // EGL10.EGL_MAX_SWAP_INTERVAL,
EGL10.EGL_LUMINANCE_SIZE,
EGL10.EGL_ALPHA_MASK_SIZE,
EGL10.EGL_COLOR_BUFFER_TYPE,
EGL10.EGL_RENDERABLE_TYPE,
0x3042 // EGL10.EGL_CONFORMANT
};
String[] names = {
"EGL_BUFFER_SIZE",
"EGL_ALPHA_SIZE",
"EGL_BLUE_SIZE",
"EGL_GREEN_SIZE",
"EGL_RED_SIZE",
"EGL_DEPTH_SIZE",
"EGL_STENCIL_SIZE",
"EGL_CONFIG_CAVEAT",
"EGL_CONFIG_ID",
"EGL_LEVEL",
"EGL_MAX_PBUFFER_HEIGHT",
"EGL_MAX_PBUFFER_PIXELS",
"EGL_MAX_PBUFFER_WIDTH",
"EGL_NATIVE_RENDERABLE",
"EGL_NATIVE_VISUAL_ID",
"EGL_NATIVE_VISUAL_TYPE",
"EGL_PRESERVED_RESOURCES",
"EGL_SAMPLES",
"EGL_SAMPLE_BUFFERS",
"EGL_SURFACE_TYPE",
"EGL_TRANSPARENT_TYPE",
"EGL_TRANSPARENT_RED_VALUE",
"EGL_TRANSPARENT_GREEN_VALUE",
"EGL_TRANSPARENT_BLUE_VALUE",
"EGL_BIND_TO_TEXTURE_RGB",
"EGL_BIND_TO_TEXTURE_RGBA",
"EGL_MIN_SWAP_INTERVAL",
"EGL_MAX_SWAP_INTERVAL",
"EGL_LUMINANCE_SIZE",
"EGL_ALPHA_MASK_SIZE",
"EGL_COLOR_BUFFER_TYPE",
"EGL_RENDERABLE_TYPE",
"EGL_CONFORMANT"
};
int[] value = new int[1];
for (int i = 0; i < attributes.length; i++) {
int attribute = attributes[i];
String name = names[i];
if ( egl.eglGetConfigAttrib(display, config, attribute, value)) {
Log.w(TAG, String.format(" %s: %d\n", name, value[0]));
} else {
// Log.w(TAG, String.format(" %s: failed\n", name));
while (egl.eglGetError() != EGL10.EGL_SUCCESS);
}
}
}
// Subclasses can adjust these values:
protected int mRedSize;
protected int mGreenSize;
protected int mBlueSize;
protected int mAlphaSize;
protected int mDepthSize;
protected int mStencilSize;
private int[] mValue = new int[1];
}
I attach it with setEGLConfigChooser(new ConfigChooser(5, 6, 5, 0, 0, 0)).Context factory:
private static class ContextFactory implements GLSurfaceView.EGLContextFactory {
private static int EGL_CONTEXT_CLIENT_VERSION = 0x3098;
public EGLContext createContext(EGL10 egl, EGLDisplay display, EGLConfig eglConfig) {
Log.w(TAG, "creating OpenGL ES 2.0 context");
checkEglError("Before eglCreateContext", egl);
int[] attrib_list = {EGL_CONTEXT_CLIENT_VERSION, 2, EGL10.EGL_NONE };
EGLContext context = egl.eglCreateContext(display, eglConfig, EGL10.EGL_NO_CONTEXT, attrib_list);
checkEglError("After eglCreateContext", egl);
return context;
}
public void destroyContext(EGL10 egl, EGLDisplay display, EGLContext context) {
egl.eglDestroyContext(display, context);
}
}
I can provide other parts of my code if necessary.
Results.
While the usual, valid result is just black screen (the black, empty texture is overlapping the red background), on S4 Exynos the screen looks like this (the arrow on the right is just system button):
So here is the question. How to fix the problem, so the app is displaying the same thing different devices?

I was able to fix my code thanks to RetoKoradi suggestion. The problem was that I've used fixed locations of uniforms in shaders (0 and 1). I'm not sure why this worked on most of deviced and on some not tho.
So instead of calls like:
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(Vertex), 0);
glEnableVertexAttribArray(0);
I'm now using:
_posAttribLocation = glGetAttribLocation(_shaderProgram, "a_position");
to store location of uniform after shader program is ready and using it instead of fixed one:
glVertexAttribPointer(_posAttribLocation, 2, GL_FLOAT, GL_FALSE, sizeof(Vertex), 0);
glEnableVertexAttribArray(_posAttribLocation);

Antialiasing in OpenGL ES 2.0?

Is there a way to implement Antialiasing technique in OpenGL ES 2.0? I have goggled and found few methods but there was no change in the output.
In the worst case, I've planned to implement multiple pass rendering, to smooth the edges in fragment shader, by displaying average colour of the pixels around every pixel, but it costs more GPU performance.
Any suggestions?

A lot of devices support MSAA (Multi-Sample Anti-Aliasing). To take advantage of this feature, you have to choose a EGLConfig that has multisampling.
On Android, if you use GLSurfaceView, you will have to implement your own EGLConfigChooser. You can then use EGL functions, particularly eglChooseConfig() to find a config you like.
The following code is untested, but it should at least sketch how this can be implemented. In the constructor of your GLSurfaceView derived class, before calling setRenderer(), add:
setEGLConfigChooser(new MyConfigChooser());
Then implement MyConfigChooser. You can make this a nested class inside your GLSurfaceView:
class MyConfigChooser implements GLSurfaceView.EGLConfigChooser {
#Override
public EGLConfig chooseConfig(EGL10 egl, EGLDisplay display) {
int attribs[] = {
EGL10.EGL_LEVEL, 0,
EGL10.EGL_RENDERABLE_TYPE, 4, // EGL_OPENGL_ES2_BIT
EGL10.EGL_COLOR_BUFFER_TYPE, EGL10.EGL_RGB_BUFFER,
EGL10.EGL_RED_SIZE, 8,
EGL10.EGL_GREEN_SIZE, 8,
EGL10.EGL_BLUE_SIZE, 8,
EGL10.EGL_DEPTH_SIZE, 16,
EGL10.EGL_SAMPLE_BUFFERS, 1,
EGL10.EGL_SAMPLES, 4, // This is for 4x MSAA.
EGL10.EGL_NONE
};
EGLConfig[] configs = new EGLConfig[1];
int[] configCounts = new int[1];
egl.eglChooseConfig(display, attribs, configs, 1, configCounts);
if (configCounts[0] == 0) {
// Failed! Error handling.
return null;
} else {
return configs[0];
}
}
}
You will obviously want to substitute the specific values you need for your configuration. In reality, it's much more robust to call eglChooseConfig() with a small set of strictly necessary attributes, let it enumerate all configs that match those attributes, and then implement your own logic to choose the best among them. The defined behavior of eglChooseConfig() is kind of odd already (see documentation), and there's no telling how GPU vendors implement it.
On iOS, you can set this property on your GLKView to enable 4x MSAA:
[view setDrawableMultisample: GLKViewDrawableMultisample4X];
There are other antialiasing approaches you can consider:
Supersampling: Render to a texture that is a multiple (typically twice) the size of your final render surface in each direction, and then downsample it. This uses a lot of memory, and the overhead is substantial. But if it meets your performance requirements, the quality will be excellent.
Old school: Render the frame multiple times with slight offsets, and average the frames. This was commonly done with the accumulation buffer in the early days of OpenGL. The accumulation buffer is obsolete, but you can do the same thing with FBOs. See the section "Scene Antialiasing" under "The Framebuffer" in the original Red Book for a description of the method.

On Android platform, you can download this OpenGL demo apps source code from GDC 2011: it contains lots of best practices and show you how to do multisampling, including coverage antialiasing.
What you need to do is just customize GLSurfaceView.EGLConfigChooser and set this chooser:
// Set this chooser before calling setRenderer()
setEGLConfigChooser(new MultisampleConfigChooser());
setRenderer(mRenderer);
MultisampleConfigChooser.java sample code below:
package com.example.gdc11;
import javax.microedition.khronos.egl.EGL10;
import javax.microedition.khronos.egl.EGLConfig;
import javax.microedition.khronos.egl.EGLDisplay;
import android.opengl.GLSurfaceView;
import android.util.Log;
// This class shows how to use multisampling. To use this, call
// myGLSurfaceView.setEGLConfigChooser(new MultisampleConfigChooser());
// before calling setRenderer(). Multisampling will probably slow down
// your app -- measure performance carefully and decide if the vastly
// improved visual quality is worth the cost.
public class MultisampleConfigChooser implements GLSurfaceView.EGLConfigChooser {
static private final String kTag = "GDC11";
#Override
public EGLConfig chooseConfig(EGL10 egl, EGLDisplay display) {
mValue = new int[1];
// Try to find a normal multisample configuration first.
int[] configSpec = {
EGL10.EGL_RED_SIZE, 5,
EGL10.EGL_GREEN_SIZE, 6,
EGL10.EGL_BLUE_SIZE, 5,
EGL10.EGL_DEPTH_SIZE, 16,
// Requires that setEGLContextClientVersion(2) is called on the view.
EGL10.EGL_RENDERABLE_TYPE, 4 /* EGL_OPENGL_ES2_BIT */,
EGL10.EGL_SAMPLE_BUFFERS, 1 /* true */,
EGL10.EGL_SAMPLES, 2,
EGL10.EGL_NONE
};
if (!egl.eglChooseConfig(display, configSpec, null, 0,
mValue)) {
throw new IllegalArgumentException("eglChooseConfig failed");
}
int numConfigs = mValue[0];
if (numConfigs <= 0) {
// No normal multisampling config was found. Try to create a
// converage multisampling configuration, for the nVidia Tegra2.
// See the EGL_NV_coverage_sample documentation.
final int EGL_COVERAGE_BUFFERS_NV = 0x30E0;
final int EGL_COVERAGE_SAMPLES_NV = 0x30E1;
configSpec = new int[]{
EGL10.EGL_RED_SIZE, 5,
EGL10.EGL_GREEN_SIZE, 6,
EGL10.EGL_BLUE_SIZE, 5,
EGL10.EGL_DEPTH_SIZE, 16,
EGL10.EGL_RENDERABLE_TYPE, 4 /* EGL_OPENGL_ES2_BIT */,
EGL_COVERAGE_BUFFERS_NV, 1 /* true */,
EGL_COVERAGE_SAMPLES_NV, 2, // always 5 in practice on tegra 2
EGL10.EGL_NONE
};
if (!egl.eglChooseConfig(display, configSpec, null, 0,
mValue)) {
throw new IllegalArgumentException("2nd eglChooseConfig failed");
}
numConfigs = mValue[0];
if (numConfigs <= 0) {
// Give up, try without multisampling.
configSpec = new int[]{
EGL10.EGL_RED_SIZE, 5,
EGL10.EGL_GREEN_SIZE, 6,
EGL10.EGL_BLUE_SIZE, 5,
EGL10.EGL_DEPTH_SIZE, 16,
EGL10.EGL_RENDERABLE_TYPE, 4 /* EGL_OPENGL_ES2_BIT */,
EGL10.EGL_NONE
};
if (!egl.eglChooseConfig(display, configSpec, null, 0,
mValue)) {
throw new IllegalArgumentException("3rd eglChooseConfig failed");
}
numConfigs = mValue[0];
if (numConfigs <= 0) {
throw new IllegalArgumentException("No configs match configSpec");
}
} else {
mUsesCoverageAa = true;
}
}
// Get all matching configurations.
EGLConfig[] configs = new EGLConfig[numConfigs];
if (!egl.eglChooseConfig(display, configSpec, configs, numConfigs,
mValue)) {
throw new IllegalArgumentException("data eglChooseConfig failed");
}
// CAUTION! eglChooseConfigs returns configs with higher bit depth
// first: Even though we asked for rgb565 configurations, rgb888
// configurations are considered to be "better" and returned first.
// You need to explicitly filter the data returned by eglChooseConfig!
int index = -1;
for (int i = 0; i < configs.length; ++i) {
if (findConfigAttrib(egl, display, configs[i], EGL10.EGL_RED_SIZE, 0) == 5) {
index = i;
break;
}
}
if (index == -1) {
Log.w(kTag, "Did not find sane config, using first");
}
EGLConfig config = configs.length > 0 ? configs[index] : null;
if (config == null) {
throw new IllegalArgumentException("No config chosen");
}
return config;
}
private int findConfigAttrib(EGL10 egl, EGLDisplay display,
EGLConfig config, int attribute, int defaultValue) {
if (egl.eglGetConfigAttrib(display, config, attribute, mValue)) {
return mValue[0];
}
return defaultValue;
}
public boolean usesCoverageAa() {
return mUsesCoverageAa;
}
private int[] mValue;
private boolean mUsesCoverageAa;
}
Before using this feature, you should known this will affect rendering efficiency, and may need to do a fully performance test.

glReadPixels when using PBuffers is failing in some android devices

I'm facing a problem with some opengl ES drivers, when calling glReadPixels for a Pbuffer some devices will just kill the app with no message at all. Others will give me the next trace and then freeze for around 10 seconds before killing the app.
Unable to Find Phys Addr for 0
So far the affected devices where the problem is reproducible are:
Galaxy Y, Galaxy Ace, Galaxy Mini, Galaxy Young
I've also tested the code in the next devices where it works correctly as expected, no problems at all:
Nexy 4, Nexus 7, Nexus Galaxy, SGI, SGII, SGIII, Motorola Mini-Defy, and some others more.
I've put together a quick test function which reproduces the problem. Maybe someone can spot the issue. Please this is only a test method, no reviews about it are necessary as I just put it together to allow testing the bug, if I missed something let me know.
private static void bugTest()
{
EGL10 egl = (EGL10)EGLContext.getEGL();
EGLDisplay eglDisplay = egl.eglGetDisplay(EGL10.EGL_DEFAULT_DISPLAY);
// Initialize
int[] version = new int[2];
egl.eglInitialize(eglDisplay, version);
// Query total number of configurations
int[] totalConfigurations = new int[1];
egl.eglGetConfigs(eglDisplay, null, 0, totalConfigurations);
EGLConfig[] configurationsList = new EGLConfig[totalConfigurations[0]];
int attribs[] = { EGL10.EGL_RENDERABLE_TYPE, 4 /* EGL_OPENGL_ES2_BIT */, EGL10.EGL_RED_SIZE, 1, EGL10.EGL_GREEN_SIZE, 1, EGL10.EGL_BLUE_SIZE, 1, EGL10.EGL_NONE };
if (egl.eglChooseConfig(eglDisplay, attribs, configurationsList, 1, totalConfigurations) == false)
{
Log.e(TAG, "Could not find config for GLES2");
egl.eglTerminate(eglDisplay);
return;
}
// Create the PBuffer
EGLSurface eglSurface = null;
final int surfaceWidth = 512;
final int surfaceHeight = 512;
try
{
int[] attribList = new int[] { EGL10.EGL_WIDTH, surfaceWidth, EGL10.EGL_HEIGHT, surfaceHeight, EGL10.EGL_NONE };
eglSurface = egl.eglCreatePbufferSurface(eglDisplay, configurationsList[0], attribList);
}
catch (Exception ex)
{
Log.e(TAG, "Failed to create surface");
egl.eglTerminate(eglDisplay);
return;
}
// BUG Test for glReadPixels
if (eglSurface != null)
{
// Create context
final int EGL_CONTEXT_CLIENT_VERSION = 0x3098;
final int GLES_VERSION = 2;
int[] attribList = { EGL_CONTEXT_CLIENT_VERSION, GLES_VERSION, EGL10.EGL_NONE };
EGLContext eglContext = egl.eglCreateContext(eglDisplay, configurationsList[0], EGL10.EGL_NO_CONTEXT, attribList);
if (eglContext != null)
{
// Attach context to surface
if (egl.eglMakeCurrent(eglDisplay, eglSurface, eglSurface, eglContext) == true)
{
// Perform the actual bug test
GL10 gl = (GL10)eglContext.getGL();
int buffer[] = new int[surfaceWidth * surfaceHeight];
IntBuffer wrappedBuffer = IntBuffer.wrap(buffer);
wrappedBuffer.position(0);
// BUG: Line of failure
gl.glReadPixels(0, 0, surfaceWidth, surfaceHeight, GL10.GL_RGB, GL10.GL_UNSIGNED_BYTE, wrappedBuffer);
// Also fails when using RGBA
//gl.glReadPixels(0, 0, surfaceWidth, surfaceHeight, GL10.GL_RGBA, GL10.GL_UNSIGNED_BYTE, wrappedBuffer);
}
egl.eglDestroyContext(eglDisplay, eglContext);
}
egl.eglDestroySurface(display, eglSurface);
}
egl.eglTerminate(eglDisplay);
}

Pbuffers are not supported on devices with Nvidia Tegra GPUs. The problem is their EGL driver, not your code. But there is really no good reason to use pbuffers anyway. They are obsolete. You should use FBOs instead, especially on Android. This article explains in detail why:
http://processors.wiki.ti.com/index.php/Render_to_Texture_with_OpenGL_ES
The best way to create an off-screen surface on Android is to construct a new SurfaceTexture() and pass that to eglCreateWindowSurface().

android: how to get display resolution in native code

Is it possible in android to get display dimensions in the native code?
I see that there are EGL related function:
EGLDisplay display = eglGetDisplay(EGL_DEFAULT_DISPLAY);
surface = eglCreateWindowSurface(display, config, engine->app->window, NULL);
eglQuerySurface(display, surface, EGL_WIDTH, &w);
eglQuerySurface(display, surface, EGL_HEIGHT, &h);
But I need dimension without creating any surface.

You can get the window size while processing the APP_CMD_INIT_WINDOW "app command" like this in your native activity:
static void engine_handle_cmd(struct android_app* app, int32_t cmd) {
struct engine* engine = (struct engine*)app->userData;
switch (cmd) {
case APP_CMD_INIT_WINDOW:
if (engine->app->window != NULL) {
int width = ANativeWindow_getWidth(engine->app->window);
int height = ANativeWindow_getHeight(engine->app->window);
}
Check out main.c in the native-activity sample NDK project if you want to know how to set up the engine struct & the engine_handle_cmd callback.

Below is the relevant code taken from the Google source for screen capture http://code.google.com/p/androidscreenshot/source/browse/trunk/Binary/screenshot.c?r=3
the vinfo structure contains fields xres and yres.
int framebufferHandle = -1;
struct fb_var_screeninfo vinfo;
framebufferHandle = open("/dev/graphics/fb0", O_RDONLY);
if(framebufferHandle < 0)
{
printf("failed to open /dev/graphics/fb0\n");
// handle error
}
if(ioctl(framebufferHandle, FBIOGET_VSCREENINFO, &vinfo) < 0)
{
printf("failed to open ioctl\n");
// handle error
}
fcntl(framebufferHandle, F_SETFD, FD_CLOEXEC);

if you're looking for the pixel values height_pixels and width_pixels are probs what you're looking for. See the developer docs for more info:
http://developer.android.com/reference/android/util/DisplayMetrics.html

Detect if OpenGl ES 2.0 is available or not

I'm creating an application for Android for API levels >= 7. One screen uses a GLSurfaceView with OpenGL ES 2.0 through the ndk. How can I detect if opengl 2.0 is available? I can't use android:glEsVersion="0x00020000" in my AndroidManifest.xml because I have to support all phones with API levels >= 7. If there is no support for 2.0, I will be showing a static screen.
I'm using similar code from the hello-gl2 sample app that comes with the ndk. In GL2JNIView, when it sets the Opengl context, if it doesn't find an appropriate opengl config (in my case a config that requires opengl es 2.0) it throws an IllegalArgumentException("No configs match configSpec") and the app crashes. I can't find a way to intercept that exception and do something else on that screen. Any ideas?

Here's what I found in internets:
private boolean checkGL20Support( Context context )
{
EGL10 egl = (EGL10) EGLContext.getEGL();
EGLDisplay display = egl.eglGetDisplay(EGL10.EGL_DEFAULT_DISPLAY);
int[] version = new int[2];
egl.eglInitialize(display, version);
int EGL_OPENGL_ES2_BIT = 4;
int[] configAttribs =
{
EGL10.EGL_RED_SIZE, 4,
EGL10.EGL_GREEN_SIZE, 4,
EGL10.EGL_BLUE_SIZE, 4,
EGL10.EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT,
EGL10.EGL_NONE
};
EGLConfig[] configs = new EGLConfig[10];
int[] num_config = new int[1];
egl.eglChooseConfig(display, configAttribs, configs, 10, num_config);
egl.eglTerminate(display);
return num_config[0] > 0;
}
Source: http://www.badlogicgames.com/wordpress/?p=343

Maybe this can help
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
// Check if the system supports OpenGL ES 2.0.
final ActivityManager activityManager = (ActivityManager)getSystemService(Context.ACTIVITY_SERVICE);
final ConfigurationInfo configurationInfo = activityManager.getDeviceConfigurationInfo();
final boolean supportsEs2 = configurationInfo.reqGlEsVersion >= 0x20000;
if (supportsEs2)
{
// Request an OpenGL ES 2.0 compatible context.
}
else
{
// This is where you could create an OpenGL ES 1.x compatible
// renderer if you wanted to support both ES 1 and ES 2.
}
}

From the Android CTS's (Compatibility Test Suite) OpenGlEsVersionTest.java:
private static int getVersionFromPackageManager(Context context) {
PackageManager packageManager = context.getPackageManager();
FeatureInfo[] featureInfos = packageManager.getSystemAvailableFeatures();
if (featureInfos != null && featureInfos.length > 0) {
for (FeatureInfo featureInfo : featureInfos) {
// Null feature name means this feature is the open gl es version feature.
if (featureInfo.name == null) {
if (featureInfo.reqGlEsVersion != FeatureInfo.GL_ES_VERSION_UNDEFINED) {
return getMajorVersion(featureInfo.reqGlEsVersion);
} else {
return 1; // Lack of property means OpenGL ES version 1
}
}
}
}
return 1;
}
/** #see FeatureInfo#getGlEsVersion() */
private static int getMajorVersion(int glEsVersion) {
return ((glEsVersion & 0xffff0000) >> 16);
}
It actually provides a few other ways as well and the test verifies that they all return the same results.